Large amounts of high-purity nitrogen are conventionally used for various applications in the semiconductor industry. In investigation of the breakdown of these applications of high-purity nitrogen reveals that high-purity nitrogen is being used in a large amount in locations that do not necessarily require such. For example, although high-purity nitrogen gas is presently used for the sealing gas of pure water tanks used for washing semiconductors, in the case of not controlling the amount of dissolved oxygen, high-purity air of a prescribed purity is sufficient. Similarly, although high-purity nitrogen gas is also used for the bubbling gas for regeneration of an ion exchange resin for production of ultra-pure water, high-purity air of a prescribed purity can be used provided such air is able to be obtained.
In addition, although high-purity nitrogen is used in air guns and semiconductor substrate storage boxes used in various semiconductor production processes in order to avoid adherence of various types of impurities, such as hydrocarbons including oils and sulfur compounds including sulfur oxides (SO.sub.x) and the like, on semiconductor substrates (wafers), high-purity air can be used instead of this high-purity nitrogen if such impurities are removed from air. In addition, high-purity air can also be substituted for high-purity nitrogen used as the carrier gas in substrate transport systems such as Bernoulli chucks and air levitation conveyors in semiconductor production equipment.
Similarly, there are also several possible processes in which high-purity air can be used instead of high-purity nitrogen or high-purity oxygen currently used as a semiconductor material gas. For example, high-purity oxygen used as the diluent gas of material gases such as carbon tetrafluoride in the etching process can be substituted with high-purity air, while air can also be used instead of the high-purity nitrogen and high-purity oxygen used in the purging process of nonreducing gases, such as chlorine, hydrogen chloride and hydrogen bromide, used in semiconductor production processes, provided it has a prescribed purity.
In view of the above, attempts have been made to reduce costs by using high-purity air instead of expensive high-purity nitrogen and high-purity oxygen in various applications. The specifications of high-purity air when used in these applications are required to be such that the levels of hydrogen (H.sub.2), carbon monoxide (CO), methane (CH.sub.4 ; total hydrocarbons (THC) as methane), water (H.sub.2 O), carbon dioxide (CO.sub.2), nitrogen compounds (NO.sub.X) and sulfur compounds (SO.sub.x) and so forth are 1 ppm or less.
In addition, since there are many processes in the production of semiconductors that are maintained at constant temperature and constant humidity, such as equipment for obtaining constant temperature and constant humidity, e.g. for air conditioning and maintaining pure water temperature, their cost is a considerable amount. Consequently, these processes are considered for reducing costs. In general, steam is supplied from a boiler to serve as a heating source, and in the heating furnace for this boiler, heating is usually performed with a fuel oil/air burner. Thus, by replacing the air of this fuel oil/air burner with oxygen-rich air, it is possible to significantly increase the combustion efficiency of the heating furnace.
Moreover, although purified air, from which water and carbon dioxide have been removed, has been conventionally used for various instruments and sealing, such air has been supplied to accommodate a relatively small demand by compressing with a small compressor and so forth, and then purified with a purifier. In addition, air for instrumentation in air liquefaction separation apparatuses has normally been used by leading into an adsorber of a pre-treatment process, and then branching off a small amount of purified air.
However, since conventional air liquefaction and separation apparatuses were only able to obtain purified air by branching off a small amount of dry air for instrumentation use as described above, there were no apparatuses that are able to produce large amounts of purified air of a high purity (high-purity air) that satisfies the above-mentioned specifications as the finished product. Namely, since minute amounts of each of the above-mentioned impurities are normally present in the atmosphere, in each of the processes of air liquefaction and separation, some of these are removed while others are contained in gas that is fed in after being concentrated. Since strict specifications were required for purity with respect to high-purity nitrogen in the prior art, various innovations were made in the process to accommodate these specifications in order to obtain satisfactory purity. In addition, the remaining exhaust gas separated from the product high-purity nitrogen was extracted is released into the atmosphere with the exception of that used as regeneration gas of the above-mentioned adsorber.
Therefore, it is an object of the present invention to provide a production process and apparatus for Various types of gases for semiconductor production factories that enable production of high-purity nitrogen used in semiconductor production factories, along with producing high-purity air that satisfies the above-mentioned requirements while simultaneously producing oxygen-rich air as the finished product.